The other thing to note - while I have not used the Flash 50, I have hiked with many who have, and just observing and listening to the folks using them? I don't think I would buy one. I think the 50 or 60 liter volume is too big for the suspension on the pack. It invites packing 30-40 lbs of traditional gear in, when it's better suited to 20-25 lbs of ultralight gear. Most folks in my hiking group have traditional (5 lb tent, 3-4 lb bag, etc) gear and it will all fit. But since the suspension is in no way adjustable, and isn't as stiff or fitted as, say, a Gregory or Granite Gear, the wearer has difficulty carrying the load.

This is why you should try other types of suspension. You may find that a stiffer, more stable, more adjustable pack suits you better. And if you have not been measure, get it done. Fixed frame packs aren't for everyone - they work well for those they fit, but when they don't fit, ugh.

I am on the long side of a "short" pack frame, and the short side of a "normal/medium" - and so I am extremely careful about pack choices. Two of my current backpacks allow me to adjust the shoulder harness in inch increments to better fit my back. Not being able to fine tune the harness to my back has led to some miserable days.

I think that when you have the right pack, one that fits and carries your gear properly, you will experience an AAAAAH moment - a lot of folks I've backpacked with don't seem to realize it's possible to be comfortable with a pack on.